The present invention relates to a cylindrical battery, such as an alkaline battery or a lithium battery, in which power generating elements are accommodated in a cylindrical battery case and an opening of the battery case is sealed with a sealing member, as well as to a method for manufacturing such a cylindrical battery.
In alkaline batteries having zinc as the anode active material, there is a fear that a gas is produced inside the battery, due to the wrong charge or the corrosion of zinc, so as to increase the internal pressure of the battery and even lead to an explosion of the battery. The alkaline batteries thus generally have a burst-proof mechanism, which functions in response to an increase in internal pressure of the battery to avoid a possible explosion.
The principle of the burst-proof mechanism is to intentionally break a specific part of lowered mechanical strength, which is a portion of a sealing member to seal the opening of the battery, on the occasion of an increase in internal pressure of the battery, so as to forcibly discharge the gas outside the battery and thereby prevent the battery from being exploded.
A typical alkaline battery having a prior art burst-proof mechanism is described with FIG. 5.
A battery case 21 keeps therein a cathode mixture 22, a separator 23, and an anode 24 as power generating elements. An upper opening of the battery case 21 has a stepped portion 25, which is bent inward by an external grooving process. A sealing member 29 of a synthetic resin, 1for example, nylon, is used to seal the opening of the battery case 21, and includes an inner tubular member 30 that supports an anode collector 28, an outer tubular member 32 that is clamped by the opening end of the battery case 21, and a joint member 31 that joins the inner tubular member 30 with the outer tubular member 32. The joint member 31 has a thin wall portion 34. A metal washer 26 having a center through hole, in which the inner tubular member 30 is fitted, and an outer circumferential portion of an anode terminal plate 33 are fitted in the outer tubular member 32 of the sealing member 29. The opening end of the battery case 21 is caulked, so that the metal washer 26 and the outer circumferential portion of the anode terminal plate 33 are securely held by the outer tubular member 32. The securely held portion is fixed on the stepped portion 25 of the battery case 21.
When the internal pressure of the battery excessively increases, the thin wall portion 34 of the sealing member 29 is broken, and the gas flowing through this broken portion is discharged outside via through holes 26a and 33a respectively formed in the metal washer 26 and the anode terminal plate 33.
As clearly understood from FIG. 5, the prior art burst-proof mechanism has a rather complicated structure and located inside the battery. The space required for the burst-proof mechanism sacrifices the capacity for the power generating elements.
Once this burst-proof mechanism functions to break the thin wall portion 34 of the sealing member 29, an electrolyte leaks through the opening of the broken portion. The opening is not closed and the leakage continues. After the release of the gas, even the dischargeable battery can thus not be used any longer.
In a high temperature environment of or over 60xc2x0 C., the thin wall portion of the sealing member stretches not to be broken. This accordingly does not work as the burst-proof mechanism, and may lead to an explosion of the battery.
The primary object of the present invention is thus to provide a cylindrical battery having a burst-proof mechanism that does not sacrifice the space for power generating elements but increases the total capacity for power generating elements.
Another object of the present invention is also to provide a cylindrical battery that is continuously usable by shielding the inside of the battery from the outside again after the burst-proof mechanism functions to release the gas from the inside of the battery.
The primary object of the present invention is attained by a cylindrical battery that includes a battery case, in which power generating elements are accommodated, a sealing member that seals an opening of the battery case, and a circular groove that is disposed in the vicinity of the opening of the battery case and has a bottom bent inward the battery case, wherein the bottom of the groove has at least one gas discharge aperture that is sealed with a seal element.
The primary object and another object of the present invention are attained by a cylindrical battery that includes a battery case, in which power generating elements are accommodated, a sealing member that seals an opening of the battery case, and a circular groove that is disposed in the vicinity of the opening of the battery case and has a bottom bent inward the battery case, wherein the bottom of the groove has at least one gas discharge aperture that is sealed with an elastic ring set in the groove.